Process of heat treating metals



April 18, 1933. A. E. BELLIS PROCESS OF HEAT TREATING METALS Filed June 19, 1929 INVENTOR ARTHUR E BELL/5 F ATTOR EY Patented Apr. 18, 1933 PATENT OFFICE ARTHUR E. IBVELLIS, or BRANFORD, comvno'rrcu'r PROCESS or HEAT 'rBEATING ETALS Application filed June 19, 1929. Serial No. 372,075.

This invention relates to an improved process of heat treating metals, and more particularly for annealing and other heat treatment operations where it is necessary to {subject the metal to widely different heat temperatures. It has heretofore been the practice in the annealing of steel and other metals in wire or strip form to first pass the same through a heat treatment bath having a temperature of approximately 1500 F., to then remove the wire from said bath and immerse the same in a quenching bath contained in a second furnace or cruci ble and having a temperature of approximately 600 F. This operation not only results in loss of time in removing the metal wire from one bath to the other, but also frequently causes surface oxidation due to contact of the atmosphere with the highly 0 heated metal wire during such transfer.

It is the primary object and purpose of my present invention to provide a process of annealing or otherwise heat-treating steel wire or other metals which will entirely 5 obviate all possibility of an oxide coating forming on the surface of the wire and will also obviate the necessity. of providing separate furnaces or crucibles to contain the annealing and quenching baths.

0' In the accompanying drawing I have illustrated more or less diagrammatically one. typical furnace construction which can be utilized in carrying out the present process,

said drawing'representing a vertical section Iithrough the furnace. Referring to this drawing, it will beseen that the furnace includes a body 5, the side and base walls of which may be constructed of a suitable refractory material, said furnace body being 0 preferably, though not necessarily, of rectangular form in plan and of requisite capacity. The interior of this furnace, body is divided by a central vertical partition wall 6, said wall at its lower end 7 terminating 5 in spaced relation to the bottom of the furnace body 5. Thus it will be seen that the partition wall provides two chambers or compartments 8 and 9 respectively, communicating at their lower ends with each 0 other beneath said partition wail.

A series of gas or oil burners 10 of conventlonal form and construction may be ar' ranged adjacent to each side of' the furnace body exteriorly thereof for the purpose of maintaining the contents of the chambers 8 and 9 at a desired temperature.

In'the operation of my improved process, a low temperature bath isfirst placed'in the furnace, said bath being of relatively high specific gravity, and preferably consisting of molten lead. The level of this bath is 'ap preciably above the lower end 7 of the partition wall 6 and extends into each of the chambers 8 and 9 of the furnace.

I next place in one of the furnace chambers, in the instance illustrated the chamber 8, a bath solution of metal salts which is of comparatively low specific gravity. This salt bath solution S may correspond to that fully described in Patent. No. 1,491,510, dated April 22, 1924. As disclosed in said patent, I preferably use an eutectic mixture of two or more metal salts which is capable of being heated to a relatively high temperature without appreciable volatilization and is also of exceedingly low viscosity, thus providing for the rapid transmission of heat so that this salt bath which is superimposed upon the lead bath L may be'rapidly heated throughout the body thereof to a uniform temperature. This salt bath solution being superimposed upon that portion of the lead bath L extending into the chamber 8, forces the molten lead bath upwardly in the other of the chambers 9, said metal salt bath and the molten lead bath S however, remaining at all times unamalgamated. By means of the burners illustrated or other suitable heating apparatus, the molten lead bath is maintained ata temperature of'approximate 90 ly 600 F., while the metal salt bath material contained in the chamber 8 and superimposed upon said leadbath is maintained at a temperature of approximately 150Q F. The lead bath being of a highly viscous character, does not absorb heat very rapid ly and the'inajor portion of said molten-lead bath will remain at a relatively low temperature, though that portion thereof upon which the high temperature heating bath 100 is immediately superimposed may attain a somewhat greater temperature'than 600 F.

In practical operation of the .new process, the steel wire or other metal indicated at M is first drawn or passed downwardly through the bath of salt solution S so that it is heated to the temperature of the salt solution, namely, substantially 1500 F. and the desired physical transformation of the metal takes place. The metal is then drawn or assed under the partition wall 6 of the urnace and into and upwardly through the chamber 9 containing the bath of molten lead L. This bath being at a relatively low temperature, namel approximately 600 F. has a quenching e ect upon the metal as it passed therethrough so that the temperature of the latter is rapidly reduced. It will, of course, be understood that the length of time the metal remains in contact with the two bath materials may be regulated and con trolled as required by simply adding to the quantity of the bath materials contained in the chambers 8 and 9 respectively, until the level of the respective baths is at a desired point above the lower end of the furnace partition wall 6.

It will be readily seen that by means of the process above described, the metal is not withdrawn from the high temperature salt bath S and exposed to the atmosphere as has heretofore been the practice before immersion in the'quenching bath, but the metal is directly drawn or passed from the high temperature salt bath into and through the low temperature quenching .bath. Thus possible oxidation of the surface of the metal is avoided and there will be a minimum loss of the high temperature salt solution. It will further-be appreciated that by means of my present process, I dispense with substantially one-half-of the equipment heretofore necessary in the annealing of such metals, since I use only a single furnace for both the high and low temperature baths instead of two separate furnaces as required in the operation of the prior arts methods and processes.

I. have above made reference to a particular kind of lo temperature bath solution, which I hav found very desirable in actual practice. Insofar as the essentlal features of my present improvement are concerned, however, it is apparent that other high temperature baths of relatively low specific gravity might be employed, and 1t is likewise possible to utilize furnace structures specifically different from that whlch Ihave illustrated in the accompanyingtdraw- I ing. In other words, my present improvements are to be broadly comprehended as consisting in a process of this character wherein high and'low temperature baths "of relatively different specific gravity are employed and in which the low specific gravity bath is directly superimposed upon the bath of high specific gravity. Accordingly, it is to be understood that in actual practice I reserve the privilege of resorting to all such legitimate changes as may be fairly embodied within the spirit and scope of the invention as claimed.

I claim:

1. A process of heat treating metals-which consists in providing a low temperature lead bath, superimposing upon part of said lead bath a fused salt bath of relatively low specific gravity and maintaining said fused salt bath at a comparatively high temperature, and then passing the metal to be treated downwardly through said fused salt bath directly into and upwardly through the lead bath before exposing the metal to the atmosphere.

2. A process of heat treating metals which consists in maintaining a low temperature lead bath at its low temperature, maintaining a fused salt bath of a comparatively higher temperature at its higher temperature, while said baths are superposed on each other, andin contact with each other, the fused salt bath being above the lead bath and over part thereof, and then passing the metal to be treated downwardly through said fused salt bath directly into and through the contacting lead bath and upwardly thereof without exposing the metal to the atmosphere, until after the metal passes out of the lead bath.

3. A process of heat treating metals which consists in maintaining a low temperature lead bath at a temperature approximately 600 F., maintaining a fused salt bath of.

a comparatively higher temperature at a temperature of approximately 1500 F., while said baths are superimposed on each other and in contact with each other, the

fused salt bath and over part thereof being hereto.

ARTHUR E. BELLIS. 

